Kenya Mall Shooting-At least 30 hostages remain trapped inside an upscale mall inNairobi, Kenya, more than 24 hours after unsuspecting shoppers were met with a siege of terror when attackers dressed in black, wearing facemasks and vests, threw grenades and opened fire on unsuspecting crowds.

Kenya's interior Cabinet secretary Joseph Lenku said at least 59 people were killed and at least 175 others were injured in the attack. While more than 1,000 people were rescued from the shopping center, Kenyan forces continue to swarm the mall are as a tense standoff ensues.

"The priority is to save as many lives as possible," Lenku said.

Terror at Nairobi Mall: Kenyan President Vows to Defeat Terrorists

Overnight, a senior Obama administration official confirmed to ABC News that four Americans are amongst the injured. Two victims -- including one child – remain hospitalized, the official said.

Three British nationals are confirmed dead in the attack, as French and Canadian officials said that their nations each had two citizens killed.

Officials say there are at least 10 to 15 gunmen involved. Initially it was believed the gang were armed robbers but it soon became clear the attackers were targeting non-Muslims.

"The gunmen told Muslims to stand up and leave. They were safe, and non-Muslims would be targeted," said witness Elijah Kamau who was shopping in the mall.

Kenya Mall Shooting: Timeline of EventsThis morning, the first and second floor of Westgate Mall have been contained, as forces work to secure the ground floor and basement of the mall, a U.S. official told ABC News.

The gunmen appear to have been "contained" by responding forces, the official said. It is unclear if some of the attackers have escaped, the official said.

Terrified shoppers and staffers who were able to make their escape described a harrowing scene to Kenyan media, which involved stepping over dead bodies on the way to safety.

The gunmen hit one of the most upscale places in Nairobi.

The Westgate Mall is a destination for Kenya's elite. It bills itself as the city's premier mall, boasting that it offers customers a "first world interior" and a "safe and serene environment." It was opened in 2007 and has more than 80 stores.

Somalia's al-Qaidia-linked rebel group, al-Shabab, claimed responsibility for the attack, saying that it was in retaliation for the 2011 involvement of Kenyan forces in their country to fight the Islamic insurgents.

"They're seeking to embarrass Kenya and get them to withdraw their troops," Associated Press reporter Jason Straziuso, who is currently in Nairobi, told ABC News."These hardcore terrorists know that this generates news in Europe and America."

While Kenya's elite troops moved into position at the mall Saturday night, Straziuso said that the most important question now is how they plan to free the hostages who are held up inside.

The U.S. Embassy in Nairobi suspended all U.S government temporary personnel, and told Mission personnel to shelter in place, avoid the Westgate mall area and avoid demonstrations or gatherings as the situation, according to its Facebook page.

State Department Deputy Spokeswoman Marie Harf said U.S. officials were closely monitoring the situation.

"We condemn this senseless act of violence that has resulted in death and injury for many innocent men, women, and children. Our condolences go out to the families and friends of all victims. We have reports of American citizens injured in the attack, and the U.S. Embassy is actively reaching out to provide assistance," Harf said in a statement.